International Archives of Photogrammetry and Remote Sensing, Vol. 32, Part 3W14, La Jolla, CA, 9-11 Nov. 1999 
    
LASER DATA FOR VIRTUAL LANDSCAPE GENERATION 
Norbert Haala, Claus Brenner 
Institute of Photogrammetry 
University of Stuttgart 
Germany 
Norbert. Haala@ifp.uni-stuttgart.de 
Commission III, Working Group 5 and 2 
KEY WORDS: building reconstruction, laser scanning, urban models 
ABSTRACT 
Within this article a procedure for the automatic generation of 3D city models is presented. For that purpose existing ground plans 
provided from a 2D GIS and height data measured by airborne laser scanning are combined. The presented approach can be applied 
for a fully automatic reconstruction of an urban model, for interactive control and correction of these automatically generated results 
and for a semi-automatic data capture. The results are 3D CAD models of the buildings. By an optional mapping of terrestrial or 
aerial images onto the reconstructed facades, virtual city models can be generated. 
1 INTRODUCTION 
One of the main tasks in photogrammetry is the efficient data 
capture for the generation of realistic representations of the real 
world. A great impact on the future demands to these 
geographic data bases can be expected due to the great success 
of the World Wide Web. Amongst other things, this success 
also resulted in a wide spread of international standards for the 
description of 3D worlds like the Virtual Reality Modeling 
Language (VRML). Additionally supported by the free 
availability of VRML-browsers, 3D visualization is now 
feasible for each standard user. Thus, the spread of applications, 
which are based on the access and visualization of virtual 3D 
worlds will increase tremendously. Possible scenarios are 
tourism information systems, which can help the potential 
visitor to plan trips as a preview afore his actual journey using 
virtual reality techniques. Hotel reservation systems can be 
integrated in order to give the user an impression of the hotel's 
surrounding in a virtual 3D environment. Due to the increasing 
power of personal digital assistants (PDA) also systems for a 
personal navigation are imaginable, where the user's route is not 
only overlaid to a 2D map, but is presented much more realistic 
in a 3D virtual model. 
All these applications will result in a great demand for the 
production of virtual city models and landscapes, presuming the 
availability of tools for efficient data capture. The development 
of these tools has been in the focus of a number of research 
activities and has led to a number of automatic and semi- 
automatic approaches (Gruen, Baltsavias and Henricson, 1997). 
Even though fully automatic procedures have been applied 
successfully for a number of individual data sets, it is generally 
agreed that their employment in a production environment can 
not be expected in the predictable future. Consequently, 
research and development has been concentrated to semi- 
automatic procedures. A second common trend is the 
integration of multiple data sources in order to make use of 
different and complementary types of information. In our 
approach an automatic data collection for virtual landscape 
generation is enabled by the combination of Digital Surface 
Models (DSM), which for our purpose is obtained by airborne 
laser scanning with a 2D GIS. 
    
Despite the high quality of laser DSM the automatic 
interpretation of this data in order to reconstruct objects like 
buildings, which are represented in that data set, remains a very 
pretentious problem. In our approach this interpretation is 
supported by the additional use of already existing ground 
plans. Since these groundplans implicitly contain information 
acquired by a human operator, the procedure can be 
denominated as semi-automatic approach. On the other hand, if 
the algorithm has access to the ground plans and the laser DSM, 
the 3D city models are generated without any further 
interaction. In that sense the procedure can be denominated as a 
fully automatic approach. 
2 ACQUISITION OF VIRTUAL CITY MODELS 
Within the approach the reconstructed buildings are represented 
by general polyhedrons. This presumes that all buildings can be 
described by straight lines and plane surfaces. In order to 
capture these polyhedral building models two major steps have 
to be performed. 
e A 3D measurement, which — in our case - is based on 
height data provided by airborne laser scanning. 
Alternatively, 3D points or lines can be derived from stereo 
imagery. 
e A structuring, i.e. the acquisition of topological relations 
between the measured 3D primitives in order to get a 
CAD-like representation of the reconstructed objects. This 
structuring also implies a semantic attributation in order to 
separate the captured primitives into different object 
categories. In addition to the separation, a selection of 
primitives, which are finally used for the description of the 
respective objects can be necessary. 
Frequently both steps are combined in a common process. In the 
algorithm described by Gülch, Müller and Läbe (1999) basic 
primitives are used for the representation of the buildings, 
which are selected and approximately fitted to the image by a 
human operator. These building primitives, which are also 
applied in our approach, already define the topological structure 
of the measured 3D points and lines. In contrast to that in the 
approach described in this paper both steps are separated and 
based on different data sets. For the required 3D measurement